1. Field of the Invention
The present invention relates to chip antennas, and in particular relates to a chip antenna for mobile communication units such as portable telephone terminals and pagers and a chip antenna for local area networks (LANs).
2. Description of the Related Art
It is important for antennas for use in mobile communication units and LANs to be small-sized. As one of the antennas satisfying such a demand, a helical-type chip antenna is known.
An example of a conventional helical-type chip antenna is shown in FIGS. 9 and 10. A chip antenna 100 comprises a rectangular-solid dielectric base body 121, an antenna line 130 disposed in the dielectric base body 121, a feed terminal 110, and a fixing terminal 111. One end 134 of the antenna line 130 is electrically connected to the feed terminal 110 and the other end 135 is unconnected.
The antenna line 130 is formed by alternately connecting a conductor pattern 131 and a via hole 132 in series. The antenna line 130 has a helical structure having a uniform width and height (or diameter) and the pitch P, and is wound about a straight axis CL in the horizontal direction (direction of arrow X in the drawing).
In order to enable a chip antenna also to be used at low frequencies, the chip antenna is generally required to reduce the resonance frequency. One of the methods for reducing the resonance frequency of the chip antenna is to decrease the spiral pitch of the antenna line.
However, since in the conventional chip antenna 100, adjacent via holes 132 are close to each other, there is a problem that the spiral pitch of the antenna line 130 cannot be reduced much due to limitation in manufacturing.
Accordingly, it is an object of the present invention to provide a chip antenna capable of reducing the spiral pitch of an antenna line so that it is smaller than that of a conventional chip antenna.
In order to achieve the above-mentioned object, in accordance with a first aspect of the present invention, a chip antenna comprises a base body, an antenna line disposed in the base body and being spirally wound, and a feed terminal disposed on a surface of the base body and being electrically connected to one end of the antenna line, wherein the antenna line has a winding axis which curves in a zigzag manner.
In accordance with a second aspect of the present invention, a chip antenna comprises a base body, an antenna line disposed in the base body and being spirally wound, and a feed terminal disposed on a surface of the base body and being electrically connected to one end of the antenna line, wherein the antenna line has a substantially straight winding axis, and adjacent wound portions have a different width or diameter.
More specifically, the antenna line may be formed by electrically connecting a plurality of conductor patterns disposed in the base body in series by via holes which are arranged in the base body in a staggered arrangement.
By the structures described above, the minimum spiral pitch of the antenna line can be smaller than that of a conventional antenna, thereby enabling the resonance frequency of the chip antenna to be reduced to less than that of a conventional chip antenna.
A chip antenna according to the present invention may further comprise an opposing conductor for adjusting the resonance frequency, wherein the opposing conductor opposes at least one of the plurality of conductor patterns forming the antenna line and is electrically connected to part of the plurality of conductor patterns. Thereby, when the area of the opposing conductor for adjusting the resonance frequency is changed, the resonance frequency of the chip antenna can be adjusted without changing the number of winding turns of the antenna line.